Fact sheets

Elderly people and those with heart or lung disease — such as asthma, emphysema and chronic bronchitis — are particularly sensitive to air pollutants. When pollution levels are high, sensitive people may experience symptoms after only one or two hours outdoors.

Children and active adults are also at a greater risk because they typically spend more time outdoors. Children tend to be more sensitive than adults because they breathe faster.

Exposure to ozone can irritate the nose and throat and cause chest tightness, coughing and wheezing. Increases in ozone levels in Canada have been linked to increased mortality, emergency hospital visits and admissions for respiratory problems. In sensitive people, the stress of ozone exposure can be particularly damaging. There is also evidence that ozone heightens the sensitivity of asthmatics to allergens.

Many of the adverse health effects resulting from exposure to particulate matter are similar to those for ozone, and are specific to the cardio-respiratory (heart - lung) system. The smaller the particle, the deeper into the lungs it can penetrate.

Health studies have focused on two groups of airborne particles that have proven harmful, even at very low levels:

PM10 (particulate matter less than 10 microns across): These particles measure about 1/8 the width of a human hair and are composed primarily of soil, soot and dust from construction and roadways and agriculture.

PM2.5 (particulate matter less than 2.5 microns across): These very fine particles cause the greatest concern. They penetrate deep into the lungs, where they cause irritation and can exacerbate lung disease. They are also responsible for reduced visibility. PM 2.5 is derived primarily from common air pollutants, such as sulphur dioxide, nitrogen oxide, and volatile organic compounds. Chemical reactions in polluted air convert these gases into particles of sulphate, nitrate and organic compounds — or into minute liquid droplets of sulphuric or nitric acid.

Recent studies have identified strong links between high levels of these airborne particles and increased hospital admissions for heart and respiratory problems, as well as higher death rates from these ailments. Other studies on animals have indicated that ozone exposure decreases the lungs' ability to ward off disease.